The present invention relates to improvements in hydrodynamic retarder or brake systems, especially to improvements in hydrodynamic brake systems for wheels or analogous rotary parts which are not or need not be driven by motors, engines or other types of prime movers. Examples of such rotary parts are certain wheels of aircraft, certain wheels of automotive land vehicles and the wheels of trailers which can be hitched to tractors, trucks or other types of towing vehicles.
A hydrodynamic brake system for the wheels of vehicles or the like comprises a bladed stator and a bladed rotor which latter defines with the stator a toroidal working chamber for a hydraulic brake fluid. In many instance, the stator and the rotor of a hydrodynamic brake system are mounted within the confines of the wheel (i.e., they do not extend axially beyond the rim which carries the tire) and are coaxial with the wheel. The brake system further comprises a reservoir for brake fluid, conduit means which connects the reservoir with the working chamber to provide a path for circulation of the fluid, a heat exchanger installed in the conduit means and serving to cool the fluid on its way from and back into the working chamber, and means for admitting compressed air into the reservoir to thus compel the fluid to flow into the working chamber when the system is to produce a braking action. The intensity of the breaking action depends on the extent to which the working chamber is filled with hydraulic fluid while the rotor rotates relative to the stator.
German Offenlegungsschrift No. 2,158,872 discloses a hydrodynamic brake system wherein a shaft which drives the rotor rotates independently of the wheel to be braked. The torque-transmitting connection between the hub of the wheel and the shaft for the rotor of the brake system includes a planetary transmission which insures that the rotational speed of the rotor greatly exceeds the rotational speed of the wheel. This enhances the torque absorption capability of the brake system; however, a speed increaser (especially a planetary transmission) contributes significantly to the bulk as well as the initial and maintenance cost of the brake system, not only because the transmission is expensive but also because the brake system must employ a discrete shaft for the rotor and reliable bearings for the shaft. Moreover, the wheel must include a specially designed hub which can accommodate the stator and the rotor, i.e., the wheel cannot be assembled of standard components. This, in turn, normally necessitates the provision of specially designed bearings for the modified hub. The just discussed publication does not describe the heat exchanger, the reservoir for brake fluid and/or the means for forcing brake fluid into the working chamber; however, the design of the wheel, stator, rotor and planetary transmission is such that the non-illustrated reservoir, heat exchanger and means for forcing the fluid into the working chamber cannot find adequate room within the confines of the wheel, i.e., they are probably remote from the wheel. Reference may be had to U.S. Pat. No. 2,963,118 to Booth et al. which discloses a hydrodynamic brake system wherein the reservoir, the heat exchanger and the means for forcing compressed air into the reservoir are remote from the housing for the stator and rotor means of the brake system.